1. Bioenergetics

2. Objectives
Discuss the functions of the cell membrane, nucleus, and mitochondria.
Define the following terms: (1) endergonic reactions, (2) exergonic reactions, (3) coupled reactions, and (4) bioenergetics.
Describe the role of enzymes as catalysts in cellular chemical reactions.
List and discuss the nutrients that are used as fuels during exercise.
Identify the high-energy phosphates.

3. Objectives
Discuss the biochemical pathways involved in anaerobic ATP production.
Discuss the aerobic production of ATP.
Describe the general scheme used to regulate metabolic pathways involved in bioenergetics.
Discuss the interaction between aerobic and anaerobic ATP production during exercise.
Identify the enzymes that are considered rate limiting in glycolysis and the Krebs cycle.

4. Introduction Metabolism
Sum of all chemical reactions that occur in the body
Anabolic reactions
Synthesis of molecules
Catabolic reactions
Breakdown of molecules
Bioenergetics
Converting foodstuffs (fats, proteins, carbohydrates) into energy

5. Cell Structure Cell membrane
Semipermeable membrane that separates the cell from the extracellular environment
Nucleus
Contains genes that regulate protein synthesis
Molecular biology
Cytoplasm
Fluid portion of cell
Contains organelles
Mitochondria

6. A Typical Cell and Its Major Organelles
Cell Structure
A Typical Cell and Its Major Organelles
Figure 3.1

7. Cell Structure
In Summary
Metabolism is defined as the total of all cellular reactions that occur in the body; this includes both the synthesis of molecules and the breakdown of molecules.
Cell structure includes the following three major parts: (1) cell membrane, (2) nucleus, and (3) cytoplasm (called sarcoplasm in muscle).
The cell membrane provides a protective barrier between the interior of the cell and the extracellular fluid.
Genes (located within the nucleus) regulate protein synthesis within the cell.
The cytoplasm is the fluid portion of the cell and contains numerous organelles

8. A Closer Look 3.1 Molecular Biology and Exercise Science
Cell Structure
A Closer Look 3.1 Molecular Biology and Exercise Science
Study of molecular structures and events underlying biological processes
Relationship between genes and cellular characteristics they control
Genes code for specific cellular proteins
Process of protein synthesis
Exercise training results in modifications in protein synthesis
Strength training results in increased synthesis of muscle contractile protein
Molecular biology provides “tools” for understanding the cellular response to exercise

9. Steps Leading to Protein Synthesis
Biological Energy Transformation
Steps Leading to Protein Synthesis
DNA contains information to produce proteins.
Transcription produces mRNA.
mRNA leaves nucleus and binds to ribosome.
Amino acids are carried to the ribosome by tRNA.
In translation, mRNA is used to determine the arrangement of amino acids in the polypeptide chain.
Figure 3.2

10. Cellular Chemical Reactions
Biological Energy Transformation
Cellular Chemical Reactions
Endergonic reactions
Require energy to be added
Endothermic
Exergonic reactions
Release energy
Exothermic
Coupled reactions
Liberation of energy in an exergonic reaction drives an endergonic reaction

11. The Breakdown of Glucose: An Exergonic Reaction
Biological Energy Transformation
The Breakdown of Glucose: An Exergonic Reaction
Figure 3.3

12. Coupled Reactions Biological Energy Transformation
The energy given off by the exergonic reaction powers the endergonic reaction
Figure 3.4

13. Oxidation-Reduction Reactions
Biological Energy Transformation
Oxidation-Reduction Reactions
Oxidation
Removing an electron
Reduction
Addition of an electron
Oxidation and reduction are always coupled reactions
Often involves the transfer of hydrogen atoms rather than free electrons
Hydrogen atom contains one electron
A molecule that loses a hydrogen also loses an electron and therefore is oxidized
Importance of NAD and FAD
Creating ATP

14. Oxidation-Reduction Reaction Involving NAD and NADH
Biological Energy Transformation
Oxidation-Reduction Reaction Involving NAD and NADH
Figure 3.5

15. Enzymes Catalysts that regulate the speed of reactions
Biological Energy Transformation
Enzymes
Catalysts that regulate the speed of reactions
Lower the energy of activation
Factors that regulate enzyme activity
Temperature pH
Interact with specific substrates
Lock and key model

16. Enzymes Catalyze Reactions
Biological Energy Transformation
Enzymes Catalyze Reactions
Enzymes lower the energy of activation
Figure 3.6

17. The Lock-and-Key Model of Enzyme Action
Biological Energy Transformation
The Lock-and-Key Model of Enzyme Action
Substrate (sucrose) approaches the active site on the enzyme.
Substrate fits into the active site, forming enzyme-substrate complex.
The enzyme releases the products (glucose and fructose).
Figure 3.7

18. Damaged cells release enzymes into the blood
Biological Energy Transformation
Clinical Applications 3.1 Diagnostic Value of Measuring Enzyme Activity in the Blood
Damaged cells release enzymes into the blood
Enzyme levels in blood indicate disease or tissue damage
Diagnostic application
Elevated lactate dehydogenase or creatine kinase in the blood may indicate a myocardial infarction

19. Examples of the Diagnostic Value of Enzymes in Blood
Biological Energy Transformation
Examples of the Diagnostic Value of Enzymes in Blood

20. Classification of Enzymes
Biological Energy Transformation
Classification of Enzymes
Oxidoreductases
Catalyze oxidation-reduction reactions
Transferases
Transfer elements of one molecule to another
Hydrolases
Cleave bonds by adding water
Lyases
Groups of elements are removed to form a double bond or added to a double bond
Isomerases
Rearrangement of the structure of molecules
Ligases
Catalyze bond formation between substrate molecules

21. Example of the Major Classes of Enzymes
Biological Energy Transformation
Example of the Major Classes of Enzymes

22. Factors That Alter Enzyme Activity
Biological Energy Transformation
Factors That Alter Enzyme Activity
Temperature
Small rise in body temperature increases enzyme activity
Exercise results in increased body temperature pH
Changes in pH reduces enzyme activity
Lactic acid produced during exercise

23. The Effect of Body Temperature on Enzyme Activity
Biological Energy Transformation
The Effect of Body Temperature on Enzyme Activity
Figure 3.8

24. The Effect of pH on Enzyme Activity
Biological Energy Transformation
The Effect of pH on Enzyme Activity
Figure 3.9

25. Carbohydrates Glucose Glycogen Blood sugar
Fuels for Exercise
Carbohydrates
Glucose
Blood sugar
Glycogen
Storage form of glucose in liver and muscle
Synthesized by enzyme glycogen synthase
Glycogenolysis
Breakdown of glycogen to glucose

26. Fats Fatty acids Primary type of fat used by the muscle Triglycerides
Fuels for Exercise
Fats
Fatty acids
Primary type of fat used by the muscle
Triglycerides
Storage form of fat in muscle and adipose tissue
Breaks down into glycerol and fatty acids
Phospholipids
Not used as an energy source
Steroids
Derived from cholesterol
Needed to synthesize sex hormones

27. Protein Composed of amino acids
Fuels for Exercise
Protein
Composed of amino acids
Some can be converted to glucose in the liver
Gluconeogenesis
Others can be converted to metabolic intermediates
Contribute as a fuel in muscle
Overall, protein is not a primary energy source during exercise

28. Fuels for Exercise
In Summary
The body uses carbohydrate, fat, and protein nutrients consumed daily to provide the necessary energy to maintain cellular activities both at rest and during exercise. During exercise, the primary nutrients used for energy are fats and carbohydrates, with protein contributing a relatively small amount of the total energy used.
Glucose is stored in animal cells as a polysaccharide called glycogen.
Fatty acids are the primary form of fat used as an energy source in cells. Fatty acids are stored as triglycerides in muscle and fat cells.

29. High-Energy Phosphates
Adenosine triphosphate (ATP)
Consists of adenine, ribose, and three linked phosphates
Synthesis
Breakdown
ADP + Pi  ATP
ADP + Pi + Energy
ATP
ATPase

30. High-Energy Phosphates
Structure of ATP
Figure 3.10

31. Model of ATP as the Universal Energy Donor
High-Energy Phosphates
Model of ATP as the Universal Energy Donor
Figure 3.11

32. Bioenergetics Formation of ATP Phosphocreatine (PC) breakdown
Degradation of glucose and glycogen
Glycolysis
Oxidative formation of ATP
Anaerobic pathways
Do not involve O2
PC breakdown and glycolysis
Aerobic pathways
Require O2
Oxidative phosphorylation

33. Anaerobic ATP Production
Bioenergetics
Anaerobic ATP Production
ATP-PC system
Immediate source of ATP
Glycolysis
Glucose  2 pyruvic acid or 2 lactic acid
Energy investment phase
Requires 2 ATP
Energy generation phase
Produces 4 ATP, 2 NADH, and 2 pyruvate or 2 lactate
ATP + C
PC + ADP
Creatine kinase

34. Bioenergetics
The Winning Edge 3.1 Does Creatine Supplementation Improve Exercise Performance?
Depletion of PC may limit short-term, high-intensity exercise
Creatine monohydrate supplementation
Increased muscle PC stores
Some studies show improved performance in short-term, high-intensity exercise
Inconsistent results may be due to water retention and weight gain
Increased strength and fat-free mass with resistance training
Creatine supplementation does not appear to pose health risks

35. A Closer Look 3.2 Lactic Acid or Lactate?
Bioenergetics
A Closer Look 3.2 Lactic Acid or Lactate?
Terms lactic acid and lactate used interchangeably
Lactate is the conjugate base of lactic acid
Lactic acid is produced in glycolysis
Rapidly disassociates to lactate and H+
The ionization of lactic acid forms the conjugate base called lactate
Figure 3.12

36. The Two Phases of Glycolysis
Bioenergetics
The Two Phases of Glycolysis
Figure 3.13

37. Interaction Between Blood Glucose and Muscle Glycogen in Glycolysis
Bioenergetics
Interaction Between Blood Glucose and Muscle Glycogen in Glycolysis
Figure 3.14

38. Glycolysis: Energy Investment Phase
Bioenergetics
Glycolysis: Energy Investment Phase
Figure 3.15

39. Glycolysis: Energy Generation Phase
Bioenergetics
Figure 3.15

40. Hydrogen and Electron Carrier Molecules
Bioenergetics
Hydrogen and Electron Carrier Molecules
Transport hydrogens and associated electrons
To mitochondria for ATP generation (aerobic)
To convert pyruvic acid to lactic acid (anaerobic)
Nicotinamide adenine dinucleotide (NAD)
Flavin adenine dinucleotide (FAD)
NAD + 2H+  NADH + H+
FAD + 2H+  FADH2

41. NADH is “Shuttled” into Mitochondria
Bioenergetics
NADH is “Shuttled” into Mitochondria
NADH produced in glycolysis must be converted back to NAD
By converting pyruvic acid to lactic acid
By “shuttling” H+ into the mitochondria
A specific transport system shuttles H+ across the mitochondrial membrane
Located in the mitochondrial membrane

42. Conversion of Pyruvic Acid to Lactic Acid
Bioenergetics
The addition of two H+ to pyruvic acid forms NAD and lactic acid
Figure 3.16

43. In Summary ADP + Pi + Energy ATP
Bioenergetics
In Summary
The immediate source of energy for muscular contraction is the high-energy phosphate ATP. ATP is degraded via the enzyme ATPase as follows:
Formation of ATP without the use of O2 is termed anaerobic metabolism. In contrast, the production of ATP using O2 as the final electron acceptor is referred to as aerobic metabolism.
ADP + Pi + Energy
ATP
ATPase

44. Bioenergetics
In Summary
Exercising skeletal muscles produce lactic acid. However, once produced in the body, lactic acid is rapidly converted to its conjugate base, lactate.
Muscle cells can produce ATP by any one or a combination of three metabolic pathways: (1) ATP-PC system, (2) glycolysis, (3) oxidative ATP production.
The ATP-PC system and glycolysis are two anaerobic metabolic pathways that are capable of producing ATP without O2.

45. Aerobic ATP Production
Bioenergetics
Aerobic ATP Production
Krebs cycle (citric acid cycle)
Pyruvic acid (3 C) is converted to acetyl-CoA (2 C)
CO2 is given off
Acetyl-CoA combines with oxaloacetate (4 C) to form citrate (6 C)
Citrate is metabolized to oxaloacetate
Two CO2 molecules given off
Produces three molecules of NADH and one FADH
Also forms one molecule of GTP
Produces one ATP

46. The Three Stages of Oxidative Phosphorylation
Bioenergetics
The Three Stages of Oxidative Phosphorylation
Figure 3.17

47. Bioenergetics
The Krebs Cycle
Figure 3.18

48. Fats and Proteins in Aerobic Metabolism
Bioenergetics
Fats and Proteins in Aerobic Metabolism
Fats
Triglycerides  glycerol and fatty acids
Fatty acids  acetyl-CoA
Beta-oxidation
Glycerol is not an important muscle fuel during exercise
Protein
Broken down into amino acids
Converted to glucose, pyruvic acid, acetyl-CoA, and Krebs cycle intermediates

49. Bioenergetics
Relationship Between the Metabolism of Proteins, Carbohydrates, and Fats
Figure 3.19

50. Aerobic ATP Production
Bioenergetics
Aerobic ATP Production
Electron transport chain
Oxidative phosphorylation occurs in the mitochondria
Electrons removed from NADH and FADH are passed along a series of carriers (cytochromes) to produce ATP
Each NADH produces 2.5 ATP
Each FADH produces 1.5 ATP
Called the chemiosmotic hypothesis
H+ from NADH and FADH are accepted by O2 to form water

51. The Chemiosmotic Hypothesis of ATP Formation
Bioenergetics
The Chemiosmotic Hypothesis of ATP Formation
Electron transport chain results in pumping of H+ ions across inner mitochondrial membrane
Results in H+ gradient across membrane
Energy released to form ATP as H+ ions diffuse back across the membrane

52. The Electron Transport Chain
Bioenergetics
The Electron Transport Chain
Figure 3.20

53. Beta Oxidation is the Process of Converting Fatty Acids to Acetyl-CoA
Bioenergetics
Beta Oxidation is the Process of Converting Fatty Acids to Acetyl-CoA
Breakdown of triglycerides releases fatty acids
Fatty acids must be converted to acetyl-CoA to be used as a fuel
Activated fatty acid (fatty acyl-CoA) into mitochondrion
Fatty acid “chopped” into 2 carbon fragments forming acetyl-CoA
Acetyl-CoA enters Krebs cycle and is used for energy

54. Bioenergetics
Beta Oxidation
Figure 3.21

55. Bioenergetics
In Summary
Oxidative phosphorylation or aerobic ATP production occurs in the mitochondria as a result of a complex interaction between the Krebs cycle and the electron transport chain. The primary role of the Krebs cycle is to complete the oxidation of substrates and form NADH and FADH to enter the electron transport chain. The end result of the electron transport chain is the formation of ATP and water. Water is formed by oxygen-accepting electrons; hence, the reason we breathe oxygen is to use it as the final acceptor of electrons in aerobic metabolism.

56. A Closer Look 3.5 A New Look at the ATP Balance Sheet
Aerobic ATP Tally
A Closer Look 3.5 A New Look at the ATP Balance Sheet
Historically, 1 glucose produced 38 ATP
Recent research indicates that 1 glucose produces 32 ATP
Energy provided by NADH and FADH also used to transport ATP out of mitochondria.
3 H+ must pass through H+ channels to produce 1 ATP
Another H+ needed to move the ATP across the mitochondrial membrane

57. Aerobic ATP Tally Per Glucose Molecule

59. Efficiency of Oxidative Phosphorylation
One mole of ATP has energy yield of 7.3 kcal
32 moles of ATP are formed from one mole of glucose
Potential energy released from one mole of glucose is 686 kcal/mole
Overall efficiency of aerobic respiration is 34%
66% of energy released as heat
32 moles ATP/mole glucose x 7.3 kcal/mole ATP
686 kcal/mole glucose
x 100 = 34%

60. Efficiency of Oxidative Phosphorylation
In Summary
The aerobic metabolism of one molecule of glucose results in the production of 32 ATP molecules, whereas the aerobic yield for glycogen breakdown is 33 ATP.
The overall efficiency of aerobic of aerobic respiration is approximately 34%, with the remaining 66% of energy being released as heat.

61. Control of Bioenergetics
Rate-limiting enzymes
An enzyme that regulates the rate of a metabolic pathway
Modulators of rate-limiting enzymes
Levels of ATP and ADP+Pi
High levels of ATP inhibit ATP production
Low levels of ATP and high levels of ADP+Pi stimulate ATP production
Calcium may stimulate aerobic ATP production

62. Example of a Rate-Limiting Enzyme
Control of Bioenergetics
Example of a Rate-Limiting Enzyme
Figure 3.22

63. Factors Known to Affect Rate-Limiting Enzymes
Control of Bioenergetics
Factors Known to Affect Rate-Limiting Enzymes

65. Control of Bioenergetics
In Summary
Metabolism is regulated by enzymatic activity. An enzyme that regulates a metabolic pathway is termed a “rate-limiting” enzyme.
The rate-limiting enzyme for glycolysis is phosphofructokinase, while the rate-limiting enzymes for the Krebs cycle and electron transport chain are isocitrate dehydrogenase and cytochrome oxidase, respectively.
In general, cellular levels of ATP and ADP+Pi regulate the rate of metabolic pathways involved in the production of ATP. High levels of ATP inhibit further ATP production, while low levels of ATP and high levels of ADP+Pi stimulate ATP production. Evidence also exists that calcium may stimulate aerobic energy metabolism.

66. Interaction Between Aerobic/Anaerobic ATP Production
Energy to perform exercise comes from an interaction between aerobic and anaerobic pathways
Effect of duration and intensity
Short-term, high-intensity activities
Greater contribution of anaerobic energy systems
Long-term, low to moderate-intensity exercise
Majority of ATP produced from aerobic sources

67. Interaction Between Aerobic/Anaerobic ATP Production
Contribution of Aerobic/Anaerobic ATP Production During Sporting Events
Figure 3.23

68. Interaction Between Aerobic/Anaerobic ATP Production
In Summary
Energy to perform exercise comes from an interaction of anaerobic and aerobic pathways.
In general, the shorter the activity (high intensity), the greater the contribution of anaerobic energy production. In contrast, long-term activities (low to moderate intensity) utilize ATP produced from aerobic sources.